This invention relates generally to the field of fuel injectors for linear engines of combustion gas-powered tools such as those used to drive fasteners.
Combustion-powered fastening tools as are currently manufactured utilize fuel injection systems that are mechanically actuated as the tool is pushed onto the work piece. This causes problems as the operator may touch the work piece with the tool a number of times before he is ready to fire a fastener, and the resulting multiple injections cause an over-rich mixture resulting in the failure of the tool to fire. According to one embodiment of this invention, a diaphragm or piston is used to automatically actuate the fuel injector using combustion pressure or air pressure generated below the piston to provide the proper injection only if the tool has actually fired. Another embodiment of this invention further delays the injection until the tool""s trigger is released.
Another object of this invention is to integrate this diaphragm-or piston-operated fuel injection system into an existing actuator currently being used to control the exhaust valve operation as described in U.S. Pat. Nos. 4,759,318 and 4,665,868, which are both hereby incorporated by reference. A further object of this invention is to provide a fuel injection portion valving system that has no critical seals or sliding components, such as are described in U.S. Pat. No. 4,365,471 and in U.S. Pat. Nos. 6,016,946 and 6,045,024. It has been found that as well as requiring precise manufacturing techniques, these linear gating or sliding component valves are prone to wear, leakage, and lubrication problems.
In accordance with one or more embodiments of the present invention, there is provided a fuel injection system for linear engines of gas-powered tools comprising a combustion chamber, the power from which drives a piston. The system also comprises a fuel source communicating through a fuel injection valve with the combustion chamber. The fuel injection valve moves between (a) a first position allowing a charge of fuel from the source to pass to a fuel plenum while simultaneously blocking passage of the fuel from the fuel plenum to the combustion chamber and (b) a second position allowing the charge of fuel in the plenum chamber to pass to the combustion chamber while simultaneously blocking off passage of fuel from the fuel source to the fuel plenum chamber. A diaphragm actuator is provided for the injection valve, the diaphragm being actuated by compressed air beneath the piston to overcome a bias of the diaphragm normally keeping it in the second position.
In an alternative embodiment, the fuel injection valve is divided into separately operated fill and dump valves. The fill valve is operated by a similar diaphragm actuator for filling the fuel plenum in response to a tool firing. The dump valve, which interrupts the flow of fuel from the plenum chamber to the combustion chamber, operates independently of the diaphragm actuator to further control the timing of the fuel injection. Preferably, the dump valve is linked to the tool""s trigger so that the dump valve opens when the trigger is released. Timing the fuel injection to the release of the trigger assures that the combustion chamber is adequately cleared of unwanted combustion by-products before new fuel is added.
In either embodiment of the present invention, the diaphragm actuator for the injection valve or the fill valve portion of the injector valve can be actuated by combustion gases from the combustion chamber instead of by compressed air beneath the piston. The system according to the present invention provides proper injection of fuel to the combustion chamber only after the tool has been fired.